Hydraulic compositions generally comprise various chemical additives that are intended to improve their properties. Among these, generally a chemical agent is used that has the function of improving the state of dispersion of the mineral particles within the composition. This chemical agent is known by various names: “dispersant”, “liquefying agent”, “water reducing agent”, “plasticizer” or “superplasticizer”. This chemical agent makes it possible to lower the water content of hydraulic compositions, for improving the performance of hydraulic compositions, including mechanical strength. Other additives (for example setting retarders or accelerators) are optionally added in parallel in the hydraulic compositions.
There is a great variety of dispersants for hydraulic compositions. These agents vary in their chemical composition and the properties that they induce in the compositions containing them.
The dispersing properties of a dispersant in a hydraulic composition are evaluated by measuring the slump, also called workability, according to standard EN 12350-2. The workability of a concrete is an important property, which governs its placement for filling the formwork.
It is evaluated just after it is prepared, as well as at specified times after preparation, making it possible to evaluate the workability over time, also called slump retention, as well as the maximum duration of workability after preparation. It will easily be understood that there is an advantage in increasing the workability of a concrete for placement, as well as an advantage in modulating the slump retention of hydraulic compositions, for example to guarantee a workability for a long period (which notably allows the placement in the formwork to be adjusted).
Moreover, although it is important to prolong the period of workability of a concrete, this must not be done to the detriment of the performance of the concrete during hardening or in the hardened state (notably the required initial or final mechanical strength), or of the level of air entrained in the hydraulic compositions. Notably, the performance of concrete in the hardened state is evaluated by measuring the compressive strength at different times (1, 3, 7 and 28 days).
A certain number of documents of the prior art describe the use of dispersant compounds based on sulfonate functions —SO2O−. The inadequate efficacy of such products quickly led the person skilled in the art to develop new structures known by the name of comb polymers.
Other documents of the prior art in fact describe the use of comb copolymers as dispersants in hydraulic compositions. We may notably mention documents WO 02/083594, WO 2004/094336, U.S. Pat. No. 7,261,772, US 2008/087198 and WO 2006/138017. The comb copolymers are synthetic copolymers with an anionic charge on the skeleton and uncharged side chains. The side chains of the anionically charged comb polymer may comprise compounds containing a polymerized epoxide, for example an ethylene oxide, a propylene oxide and/or a 1-butylene oxide.
Documents US 2008/087198 and U.S. Pat. No. 7,261,772 propose using an amide jointly with said comb copolymers, this combination being presented as effective for dispersing mineral matter with impurities.
As for document WO 98/58887, it proposes doping the efficacy of comb polymers in cement matrixes containing clays, using organic or inorganic cations and quaternary (poly)amines, optionally alkoxylated.
As for document FR 2 887 542, it recommends employing a particular cationic polymer to neutralize the harmful effects of the clays contained in certain sands.
Document FR 2 759 704 describes the use of alkylene polyoxide compounds for dispersing carbon black, an organic material that is amorphous, hydrophobic and not electrically charged, different from the mineral fillers of the calcium carbonate type.
Document WO 97/19748 describes the use of a dispersant for dispersing pigment particles in the paint application. This agent consists of a poly(oxyethylated) and poly(oxypropylated) phosphate ester.
Documents FR 2 696 736, FR 2 943 053, FR 2 810 314, FR 2 763 065, WO 2012/140235 and WO 2013/093344 describe the use of compounds bearing a polyalkoxylated chain and one or two phosphonic amino-methylene groups as liquefying agents (or rheology extenders) for aqueous suspensions of mineral particles. Such compounds are available commercially. As an example, we may mention the products CHRYSO®Fluid in the Optima range (for example Optima 100 and Optima 175).
The article by Pourchet et al. (Influence of three types of superplasticizers on tricalciumaluminate hydration in presence of gypsum in International Conference on Superplasticizers and other chemical admixtures in concrete, Sorrento: Italy, 2006) studies the influence of the chemical structure of various superplasticizers, notably a poly(oxyethylene) diphosphonate polymer, on the hydration of cement.
The inventors realized that the performances of hydraulic compositions, evaluated by the workability of said freshly prepared composition and by the compressive strength of said composition in the hardened state, could be improved relative to the commercially available products of the alkoxylated diphosphonate type, by using a particular chemical additive, namely a polyethylene glycol geminal ester phosphate according to the invention.